Fuse links



2 Sheets-Sheet 1 FUSE LINKS E. JACKS ET AL Aug. 11, 1970 Filed May 27, 196e mw va F v Aug. 11,1970 E, JACKS EFA-L FUSE LINKS 2 sheets-sheet 2 Filed May 27. 41968 mmf Iv United States Patent() 3,524,199 FUSE LINKS Eric Jacks, .lohn Feenan, and Wilfred Clarke, Liverpool, England, assignors to The English Electric Company Limited, London, England, a British company Filed May 27, 1968, Ser. No. 732,167 Claims priority, application Great Britain, May 26, 1967 24,516/ 67 Int. Cl. H01h 85/08 U.S. Cl. 337-161 3 Claims ABSTRACT F THE DISCLOSURE Fuse links incorporating dual elements for operating dual elements for operating on both high fault currents and sustained overloads. In particular, a fuse link comprises iirst elements of strip form and a second element connected between them comprising two plate-like members. These two members are soldered to the iirst elements, and springs are provided normally to bias these members apart. The arrangement is operable such that the iirst element fuses only upon the passage of a high overcurrent whereas the two plates of the second element are operable to break contact with the iirst elements in response to the solder melting on the passage of a sustained overload current, the springs being effective to force apart these two plates under this condition.

This invention relates to fuse links, and more particularly relates to fuse links incorporating dual elements for operating on both high fault currents and sustained overloads.

From one aspect, the present invention consists in a fuse link comprising a tubular body terminated by two end caps, a iirst element of strip form, a second element comprising two planar members over-lapping the first element from opposing sides and biassed outwardly therefrom, and means for retaining the members in contact with this element against the restoring bias, the first element being operable to fuse upon the passage therethrough of a high overcurrent and the second element being operable to break contact with the first element in response to the retaining means being overcome by said bias upon the passage of a sustained overload current.

The biasing medium may be a torsion spring operable to pivot both members outwardly from the strip element and break the circuit, these members normally being secured to this element by a low melting point solder, e.g. a solder melting between 100 C. and 230 C. The solder is so selected as to melt and release the two planar members after a period dependent on the magnitude of the overload.

The second element may be centrally connected between two of the said rst elements, and all the element may be constructed from brass or copper in order to be compatible with the lead-tin solder employed, so as to avoid the production of a eutectic alloy which adversely affects the fuse characteristics The fuse is iilled with arc-quenching sand, and in order to shield the central second element from the sand, which would otherwise impair its operation, a housing is constructed to completely envelope this element. The housing may be constructed in two parts which make frictional contact with one another and clamp around the second element, the housing being spaced from the tubular walls of the fuse link and so shaped as to permit the free passage through the sand of a shunt wire bridging the two elements.

In order that the invention can be fully understood, one embodiment thereof will now be described, by way of eX- icen ample, with reference to the accompanying drawings, in which:

FIGS. 1 and 2 illustrate part-sectional plan and side elevations of the fuse link; and

FIG. 3 illustrates a cross-section through A--A in FIG. 2.

Referring now to the drawings, the fuse link comprises a tubular body 1 of insulating material e.g. vulcanised or melamine libre, terminated by two conductive spade contacts 2, 3 secured by caps 4, 5 respectively. A C-ring 6 having the same diameter as the adjacent flange on the spade contacts lies between the cap and the end washers so as to avoid any tendency on assembly for the cap to press the spade contact inwardly and possibly buckle the washers and strain the dual element. This dual element is a composite structure comprising two brass or copper elements 7, 8 designed to fuse under short-circuit or high overcurrent conditions and a central member 9 for operating on sustained overloads.

The short-circuit elements are arranged in pairs 7A, 7B and 8A, 8B each having four links notched to realise the desired fusing characteristics and bent into a box-like configuration. The outer tags 7A and 7B are secured to opposing sides of the contact 2 by solder and the inner tags 7 and 7B are soldered directly to one another, the elements 8A, 8B being arranged in the same way.

The overload member 9 comprises two copper blocks 9A, 9B which are soldered by a low melting point solder on to opposite sides of the inner tags of the short-circuit elements so as to bridge the space between them and provide a continuous electrical circuit through the fuse link. Two torsion springs 10, 11 are disposed on opposite sides of these blocks and are held in position by the ends 13, 14, of these springs being disposed in recesses at the remote ends of the blocks. Thus, in the position shown, the torsion springs 10, 11 exert on the soldered blocks a biasing force tending to separate them from the shortcircuit elements.

Disposed around this overload member is a moulded housing 15 e.g. nylon, which has twomating parts 15A, 15B which are retained together by frictional engagement, these parts being supported on the inner tags of the elements 7, 8 and completely enveloping the member 9 so as positively to exclude from it the sand filling 16 0f the fuse link. In addition, opposed sides of the two parts 15A, 15B have iiats formed in them so as to permit the free passage of a shunt wire 17 which extends between the spade contacts 2, 3.

In operation, with a high fault current flowing through the fuse link, the short-circuit elements 7 and/or 8 are designed to rupture instantaneously together with the shunt wire 17, whereas on low sustained overloads the heat developed in the central member softens the solder by which the two blocks are secured between the elements 7 and 8 and the blocks spring apart so as to break their bridged connection between these elements. The overload current then flows through the shunt wire 17 which is designed to fuse substantially instantaneously and break the circuit, this shunt Wire thus relieving the overload device from any interrupting duty.

A fuse link of the type described may be rated from say 250 to 600 volts at between 60 and 600 amperes, each short-circuiting element being of the order of 2 inches in length and having less than the four links shown, e.g. two, at the lower rating and more, e.g. five, at the higher rating. The mass of the two copper blocks 9A, 9B, which act as a heat sink on low overcurrents and thus affects the temperature at which the solder softens sufficiently for them to spring apart, is accordingly determined by the overload characteristics required. The solder employed to secure these blocks to the elements 7, 8 may conveni- 3 ently have a melting point of say between 100 C. and 230 C.

The manufacture of a fuse link of the type described is particularly facilitated by the design of the housing 15 which is self-supporting on the member 9, completely sealed, and spaced from the inner Walls of the tubular body so as to permit sand filling of the link from one end only during assembly. Furthermore, the ats on the two parts readily permit the shunt wire to be positioned on either side of the link with a good degree of clearance.

We claim:

1. A fuse link comprising a tubular body terminated by two end caps,

a pair of rst elements of strip form,

a second element secured between the rst elements and comprising two planar members overlapping the inner ends of the rst elements from opposing sides and retained in contact with them by a low melting point solder,

a torsion spring secured to said planar members and operable to urge both of said members away from one another in a pivotal manner against the restoring force of the solder, the iirst element fusing upon the passage therethrough of a high overcurrent and the second element breaking contact with one of the rst elements upon the passage of a sustained overload current in response to the solder melting and the torsion spring becoming effective to force the planar members apart,

a discrete housing disposed within the tubular body and inwardly spaced therefrom, the housing being 4 supported on the first elements and wholly enveloping both the second element and the torsion spring,

and

an arc-quenching sand filler within the tubular body,

the housing positively shielding the second element and the torsion spring from the ingress of said sand.

2. A sand-filled fuse link according to claim 1 com'- prising a shunt wire bridging the rst and second elements',

said shunt wire extending through the sand between the housing and the inner Wall of the tubular body.

3. A fuse link according to claim 1, wherein the housing is constructed from two parts making frictional contact with one another.

References Cited UNITED STATES PATENTS BERNARD A. G1LHEANY,Primary Examiner D. M. MORGAN, Assistant Examiner U.S. Cl. X.R. 

